Clouds have to be one of my favourite things to look at.  They are constantly changing, come in many forms and have an element of mystery to them.  Until the nineteenth century, they were all just called “essences” as nobody thought to classify or name the different types.

In 1802, a 30-year-old amateur meteorologist, Luke Howard, decided to categorize and name them.  He presented his findings to the Askesian Society in London, his work was accepted and is what we still use today.

I find clouds to be one of the most difficult things to paint.  The reason for this is that usually when I draw or paint anything I use a technique called the “Form Principle.”  The Form Principle is a way of representing the way light and shadow fall on objects.  This works well for painting solid objects as you think of the shape of the object you want to represent, then decide where the light source is, and this guides you as to where you put your light areas and shadows.

Unfortunately, this technique has only limited success when painting clouds.  The problem with this is you wind up with clouds that look solid – and that is not good.

When you observe clouds in the sky, the light not only hits the surface of them, it penetrates and scatters inside them; it is a phenomenon called sub-surface scattering.  If you have ever put a flashlight behind your fingers and noticed the way the light makes the outer edges of your fingers glow you have experienced what subsurface scattering is. This is the key to making clouds look believable.  Even at this point, though, you need to think about what kind of cloud it is an how its masses are formed.  The density of water droplets inside them will change the way light interacts with them.

Below, I have painted over the previous diagram.  The form layer is still there, but the light comes through the sphere spreading the highlight out to a much broader area, filling out to the edges and illuminating the area that follows the path of the light rays (the area in this diagram right below the reflected light). The area outside the sphere has a bit of a glow, but not too much.  Even though clouds aren’t solid, they often appear to have defined edges.

The diagram above still doesn’t look like a cloud, though.  What is wrong with the picture is that it is not built like a cloud.  Believe it or not, clouds do have structure.  I’ll update this post soon with some thoughts about the anatomy of clouds.

I created the two paintings above using Artrage on my iPad.  I have a few more in progress and will add them to this post soon.